This invention generally relates to down hole tools, specifically to underreamers, section mills, casing cutters, casing scrapers and drill string centralizers.
Most conventional underreamers, section mills, casing cutters, casing scrapers and drill string centralizers open via pump pressure and compression spring which actuate blades to an outward position longitudinally from the drill string. This only allows a limited small number of blades to be used and then only a limited amount of cutting surface is available to ream, cut, mill, scrape, or centralize. The present invention can be used in different forms as an underreamer, section mill, casing cutter, casing scraper or drill string centralizer but will be hereinafter collectively referred to as Underreamer. The present invention Underreamer provides for one or more turbines and rotor to actuate blades axially from the drill string, which allows more blades to be used to more effectively centralize the tool. The Underreamer also enables the blades to be larger in height than conventional tools to provide more surface area to be worn away or used which significantly increases the available time to ream, mill or cut without removing or tripping the drill string and replacing or refurbishing the tool. The Underreamer can be used with normal fluid circulation down through the drill pipe and returned to the surface via the annulus, or unlike most conventional tools can also be reverse circulated down the annulus and back to the surface via the inside of the drill string. Reverse circulation is necessary in large diameter or extended length bore holes where a large borehole volume cannot be continuously pumped clear with normal circulation due to available pumping equipment or reservoir pressures unable to sustain the pressure. An additional feature of the tool is its strength and compact length relative to conventional tools. One of the benefits to compactness is that logging or directional drilling tools or other equipment can be located closer to the leading drill bit for more accurate information. The Underreamer also has the advantage of being able to work while advancing or retreating.
Representative patents are U.S. Pat. No. 7,036,611 to Steven R. Radford, et al. and 7,650,951 to Hall et al.